1. Field of the Invention
The present invention relates to a semiconductor device provided with a tin diffusion inhibiting layer, and a manufacturing method of the same.
2. Description of the Related Art
According to WO 2003/012863, a solder ball is provided on the land of a wiring line provided on a semiconductor substrate. In this case, a plated film made of, for example, nickel is provided on the upper surface of the land of the wiring line made of copper in order to reduce contact resistance and promote the reactivity of solder. The solder ball is provided on the upper surface of the plated film.
In the meantime, although WO 2003/012863 does not describe any method of forming the plated film, parts other than the land of the wiring line are covered with an overcoat film, and the plated film smaller in thickness than the overcoat film is formed on the upper surface of the land of the wiring line within an opening formed in the overcoat film in the part of the wiring line corresponding to the land. It is therefore presumed that the plated film is formed by electroless plating.
If tin in the solder ball diffuses into the wiring line made of copper, a fragile alloy layer made of tin and copper is formed or a void is generated in the wiring line, such that the wiring line tends to be broken. Accordingly, if the plated film made of, for example, nickel is formed on the upper surface of the land of the wiring line, the plated film functions as a tin diffusion inhibiting layer.
However, in a semiconductor device such as a power supply IC which deals with a high current, the velocity of the diffusion of tin in the solder ball into the wiring line is significantly increased by an electromigration phenomenon. On the other hand, if the plated film is formed by the electroless plating, the thickness of the plated film is relatively small and is as thick as 5 μm or less owing to the characteristics of the electroless plating. In the case of sputtering, the thickness of the plated film is about 2000 to 5000 Å (0.2 to 0.5 μm). Thus, the problem of a semiconductor device such as the power supply IC which deals with a high current is that a tin diffusion inhibiting function cannot be said to be enough even if the plated film is formed on the upper surface of the land of the wiring line by the electroless plating.